Apparatus for detecting constituents in a sample and method of using the same

ABSTRACT

An apparatus for detecting constituents in a sample includes first and second drift tubes defining first and second drift regions, and a controllable electric field device within a fragmentation region coupled to the first and second drift tubes. The apparatus also includes a first ion shutter positioned between the first drift and fragmentation regions. The apparatus further includes a control system configured to regulate the first ion shutter, thereby facilitating injection of a selected portion of ions from the first drift region into the fragmentation region. The control system is also configured to regulate the controllable device to modify the selected portion of ions to generate predetermined ion fragments within the fragmentation region, thereby facilitating injection of a selected portion of the predetermined fragmented ions into the second drift region. A method of detecting constituents in a sample is facilitated through such an apparatus.

BACKGROUND

The embodiments described herein relate generally to ion mobilityspectrometer (IMS) systems and ion trap mobility spectrometer (ITMS)systems and, more particularly, to IMS and ITMS detection systems forenhancing detection of materials of interest through enhancedinformation of fragmented ions.

At least some known spectrometric detection devices include atime-of-flight (TOF) ion mobility spectrometer (IMS) detection systemand a TOF ion trap mobility spectrometer (ITMS) detection system. SuchTOF-IMS and -ITMS detection systems are used to detect trace amounts ofmaterials of interest, e.g., residues, in the presence of interferingsubstances in collected samples. In at least some known IMS and ITMSsystems, ions are generated in an ionization chamber to increase the ionpopulation therein and a retaining grid or an ion gate is maintained ata potential to induce a retention field and reduce the potential for ionleakage from the chamber. The ions are “pulsed” from the ionizationchamber into a drift region through the retaining grid or ion gate. Theions are transported through the drift region to a collector electrodeusing an electric field. Signals representative of the ion population atthe collector electrode are generated and transmitted to an analysisinstrument and/or system to determine the constituents in the collectedgas samples. Based on an ions' mass, charge, size, and shape, the ionmobility determines the migration time through the drift region which ischaracteristic of different ions, leading to the ability to distinguishdifferent analyte species.

However, many known drift tubes of IMS and ITMS systems have a limitedresolving power. As peaks generated by ions from different compoundsshare similar drift times, some of the interferences, including benignsubstances, have the same drift times as the analyte compounds ofinterest associated with an increasing number of threats programmed intothe detection library and, therefore, create false alarms. A number ofmethods and apparatus have been used to characterize the ions ofinterest and to decrease the false alarm rate which is addressed by theconcept of the reactive drift tubes.

One method proposed to decrease the false alarm rate is fragmentation,i.e., the dissociation of energetically unstable molecular ions to formion fragments of a molecule that induce a pattern in the mass spectrumor mobility spectrum used to determine structural information of theoriginal molecule. Fragmentation can be achieved through a variety ofmeans, including fragmentation induced by collision induced dissociation(CID) with selected gases injected into the flow path of the apparatus,fragmentation induced through a set of electrodes capable of generatingelectric fields with sufficiently high electric field strength tothermally form disassociated products, dissociation through laser that,depending on the required wavelength and molecules to be dissociated,uses one of photodissociation, infrared multiphoton dissociation, andthermal dissociation. Further methods of fragmentation include electroncapture and transfer methods through injection of active chemicals.

Some known IMS and ITMS systems use ion dissociation through ahigh-voltage radio-frequency (HV RF) unit positioned within the drifttube. However, such IMS and ITMS systems lack the selection of ions tobe fragmented, e.g., through a second ion shutter before the HV-RF unit.Therefore, most of the ions to be fragmented and the fragmented ionsenter the second portion of the drift region without any screening,regardless of the chemical makeup of the fragmented ions. As such, theassignment of the fragment ions to spectral patterns is complex withlittle to no discrimination. The results may be ambiguous because theability to discern the identity of the resulting fragments is limitedsince the ions to be dissociated are not separated from the other ions.In some of these known IMS and ITMS systems, operation at reducedpressures is one attempt of reducing the number of ion collisions andthus reducing the number of fragments to generate a more simplistic rawdata stream, but the simplicity of the IMS and ITMS techniques iscompromised by adding the additional hardware, such as vacuum chambersand pumps.

Some other known IMS and ITMS systems include a plurality of tandemdrift tubes with ion control grids therebetween, where one of the drifttubes includes a fragmentation device. Such tandem drift tube devicesare configured to select ions from a first drift tube through an ioncontrol grid for introduction into a second drift tube for fragmentationthrough one of laser irradiation and vapor injection to promoteselective reactions and additional analytical selectivity. However, suchmechanisms substantially form adducts with the selected ions that aretransferred to a third drift tube through another ion control grid forcharacterization therein. Also, uncontrolled movement of sample neutralsbetween mobility regions facilitates ion molecule reactions in the driftregions that further complicate the interpretation of the resultantspectra.

BRIEF DESCRIPTION

In one aspect, an apparatus for detecting constituents in a sample isprovided. The apparatus includes a first drift tube defining a firstdrift region, a second drift tube defining a second drift region, and acontrollable electric field device coupled to the first drift tube andthe second drift tube. The controllable electric field device at leastpartially defines a fragmentation region. The apparatus also includes afirst ion shutter positioned between the first drift region and thefragmentation region. The apparatus also includes a control systemcoupled to the controllable electric field device and the first ionshutter. The control system is configured to facilitate injection of aselected portion of the predetermined fragmented ions into the seconddrift region. The control system includes a processor and is alsoconfigured to regulate the first ion shutter a first predeterminedtemporal period, thereby facilitating injection of a selected portion ofions from the first drift region into the fragmentation region. Thecontrol system is further configured to regulate the controllableelectric field device to modify the selected portion of ions to generatepredetermined ion fragments within the fragmentation region.

In another aspect, a method of detecting constituents in a sample isprovided. The method includes channeling a sample gas stream to betested for constituents into an ionization region, generating aplurality of ions in the ionization region, and injecting at least aportion of the ions from the ionization region into a first driftregion. The method also includes injecting a selected portion of ionsfrom the first drift region into a fragmentation region includingregulating a first ion shutter a first predetermined temporal period,where the first ion shutter is positioned between the first drift regionand the fragmentation region. The method further includes modifying theselected portion of ions, thereby generating predetermined ion fragmentswithin the fragmentation region including regulating a controllableelectric field device positioned within the fragmentation region.

DRAWINGS

FIGS. 1-4 show exemplary embodiments of the systems and methodsdescribed herein.

FIG. 1 is a schematic view of an exemplary ion trap mobilityspectrometer (ITMS) detection system;

FIG. 2 is a schematic view of an alternative ion trap mobilityspectrometer (ITMS) detection system;

FIG. 3 is a graphical view of exemplary spectra that may be producedusing the ITMS detection systems shown in FIGS. 1 and 2; and

FIG. 4 is a graphical view of additional exemplary spectra that may beproduced using the ITMS detection systems shown in FIGS. 1 and 2.

DETAILED DESCRIPTION

The embodiments described herein provide a cost-effective system andmethod for improving detection of materials of interest from an objector person. The systems and methods described herein use a detectorhaving two sequentially arranged drift tubes which are separated byshutters facilitating ions of a user-selected, i.e., library-defineddrift time to be introduced into the second drift tube whereas otherions of a different mobility are discarded as needed. The tandemreactive IMS and ITMS devices disclosed herein facilitate multipleopportunities to isolate ions of interest including ion separation andselection in the first drift tube, predetermined modification throughfragmentation with a controllable electric field, and selectedtransmission into the second drift tube ultimately ending with specificidentification of the ions. Regulation of the electric field strengthand temperature analyte ions from one compound may dissociate and formdissociation products that can further be characterized, while ions fromanother compound may dissociate as well but form different products ormay even not dissociate at all. As such, this dissociation informationis important for providing another dimension of characterizing themobility of ions by their stability and their dissociation productswhich provides additional confidence in the presence or absence of peaksthat facilitates determining if an alarm could be generated or rejected.The results are more easily interpreted and provide more definitiveinformation that can be used for the characterization of ions since onlyions of a particular drift time are exposed to the high electric fieldand the associated fragmentation. Consequently substantially alldissociation products detected in the second drift tube originate fromthe ions selected from the first drift tube and subsequently fragmented.Moreover, the additional optional introduction of dopants facilitatesfurther modification of the selected ions through chemical reactionswith or without dissociation. As such, the systems described hereinfacilitate an additional level of selectivity that dramatically reducesthe false alarm rate from that observed on traditional IMS systems.Therefore, the portable mobility spectrometers described hereinfacilitate substance analysis with higher confidence while maintainingatmospheric pressure operation.

FIG. 1 is a schematic view of an exemplary time-of-flight (TOF) ion trapmobility spectrometer (ITMS) detection system 100 (not drawn to scale).ITMS detection system 100 includes a casing 102. ITMS detection system100 also includes a gas inlet tube 104 and a gas outlet tube 106 coupledto casing 102. In the exemplary embodiment, casing 102 includes an iontrap reactor 108 coupled in flow communication with gas inlet tube 104.Ion trap reactor 108 includes an ionizing source material (not shown),e.g., and without limitation, nickel-63 (⁶³Ni) that emits low-energybeta- (β-) particles. Alternatively, any ionizing source or ionizingsource material that enables operation of ITMS detection system 100 asdescribed herein is used. ITMS detection system 100 further includes aretaining grid 110 extending over an outlet end of ion trap reactor 108.

Casing 102 further defines a tandem reactive dual drift tube and dualshutter configuration 112. Configuration 112 includes a first drift tube114 defining a first drift field region 116 coupled in flowcommunication with ion trap reactor 108. Configuration 112 furtherincludes a series of sequential annular electrodes E1, E2, E3, E4, E5,E6, and E7 extending about first drift field region 116. Configuration112 also includes a fragmentation region 118 at least partially definedby casing 102. Fragmentation region 118 facilitates predeterminedmodifications of ions received from first drift field region 116 throughfragmentation with a controllable electric field generated by anelectric field generation device 120 that includes a high-voltageradio-frequency (HV RF) unit 122 and electrodes 124 and 126 spaced fromeach other across the diameter of fragmentation region 118. Electrodes124 and 126 are any devices that enable operation of ITMS detectionsystem 100 through production of a strong electric field, such devicesincluding, but not limited to, wire grids and other metal structuresthat generate sufficient field strength. Electric field generationdevice 120 generates electric fields of sufficient strengths andfrequencies to modify ions therein (discussed further below).

Also, in the exemplary embodiment, configuration 112 further includes afirst ion shutter 128 that at least partially defines first drift fieldregion 116 and fragmentation region 118 when energized and facilitatesflow communication between regions 116 and 118 when de-energized. Inaddition, configuration 112 includes a second drift tube 130 defining asecond drift field region 132. Configuration 112 also includes a seriesof sequential annular electrodes E8, E9, E10, E11, E12, E13, and E14extending about second drift field region 132. Second drift field region132 receives fragmented ions from fragmentation region 118. In someembodiments, configuration 112 further includes an optional second ionshutter 134 that at least partially defines second drift field region132 and fragmentation region 118 when energized and facilitates flowcommunication between regions 118 and 132 when de-energized. In otherembodiments, rather than second ion shutter 134, configuration 112further includes an optional ion trap 135 similar in design,construction, and operation as ion trap reactor 108. Such ion trap 135positioned between fragmentation region 118 and second drift fieldregion 132 is configured to provide similar operational results assecond ion shutter 134, i.e., release fragmented ions into second drifttube 130 as an alternative to using a shutter grid.

ITMS detection system 100 also includes an ion collector 136 thatincludes a collector shield grid, i.e., an aperture grid 138 and acollector electrode 140, e.g., a Faraday plate positioned justdownstream of aperture grid 138. Collector electrode 140 is coupled to aspectral analysis device 142 that includes at least onecurrent-to-voltage amplifier (not shown). ITMS detection system 100further includes an ITMS control system 144 that includes a processingdevice 146. ITMS control system 144 is operatively coupled to ion trapreactor 108, retaining grid 110, sequential annular electrodes E1-E7,electric field generation devices 120, first ion shutter 128, second ionshutter 134 (if installed), second ion trap 135 (if installed), E8-E14,aperture grid 138, collector electrode 140, and spectral analysis device142. Casing 102 also defines a collector region 148 coupled in flowcommunication with second drift field region 132 and gas outlet tube106.

As used herein, the terms “processor” and “processing device” are notlimited to just those integrated circuits referred to in the art as acomputer, but broadly refers to a microcontroller, a microcomputer, aprogrammable logic controller (PLC), an application specific integratedcircuit, and other programmable circuits, and these terms are usedinterchangeably herein. In the embodiments described herein, memory mayinclude, but is not limited to, a computer-readable medium, such as arandom access memory (RAM), and a computer-readable non-volatile medium,such as flash memory. Alternatively, a floppy disk, a compact disc-readonly memory (CD-ROM), a magneto-optical disk (MOD), and/or a digitalversatile disc (DVD) may also be used. Also, in the embodimentsdescribed herein, additional input channels may be, but are not limitedto, computer peripherals associated with an operator interface such as amouse and a keyboard. Alternatively, other computer peripherals may alsobe used that may include, for example, but not be limited to, a scanner.Furthermore, in the exemplary embodiment, additional output channels mayinclude, but not be limited to, an operator interface monitor.

Also, as used herein, the terms “software” and “firmware” areinterchangeable, and include any computer program stored in memory forexecution by personal computers, workstations, clients and servers.

Further, as used herein, the term “non-transitory computer-readablemedia” is intended to be representative of any tangible computer-baseddevice implemented in any method or technology for short-term andlong-term storage of information, such as, computer-readableinstructions, data structures, program modules and sub-modules, or otherdata in any device. Therefore, the methods described herein may beencoded as executable instructions embodied in a tangible,non-transitory, computer readable medium, including, without limitation,a storage device and/or a memory device. Such instructions, whenexecuted by a processor, cause the processor to perform at least aportion of the methods described herein. Moreover, as used herein, theterm “non-transitory computer-readable media” includes all tangible,computer-readable media, including, without limitation, non-transitorycomputer storage devices, including, without limitation, volatile andnonvolatile media, and removable and non-removable media such as afirmware, physical and virtual storage, CD-ROMs, DVDs, and any otherdigital source such as a network or the Internet, as well as yet to bedeveloped digital means, with the sole exception being a transitory,propagating signal.

Furthermore, as used herein, the term “real-time” refers to at least oneof the time of occurrence of the associated events, the time ofmeasurement and collection of predetermined data, the time to processthe data, and the time of a system response to the events and theenvironment. In the embodiments described herein, these activities andevents occur substantially instantaneously.

Processing device 146 and other processors (not shown) as describedherein process information transmitted from a plurality of electricaland electronic devices that include, without limitation, spectralanalysis device 142 and feedback devices (not shown) within ITMSdetection system 100. Memory devices (not shown) and storage devices(discussed further below) store and transfer information andinstructions to be executed by processing device 146. Such memorydevices and storage devices can also be used to store and providetemporary variables, static (i.e., non-volatile and non-changing)information and instructions, or other intermediate information toprocessing device 146 during execution of instructions by processingdevice 146. Instructions that are executed include, but are not limitedto, analysis of signals transmitted from spectral analysis device 142.The execution of sequences of instructions is not limited to anyspecific combination of hardware circuitry and software instructions.ITMS detection system 100 also includes a data storage device 150coupled to processing device 146. Data storage device 140 stores thedata generated by processing device 146, such data also retrievablethrough processing device 146.

In operation, a collection device (not shown) is coupled to gas inlettube 104 and collects gaseous samples 152 from an object of interest(not shown). In some embodiments, rather than gaseous samples, inlettube 104 channels particulate samples that are then vaporized togenerate gaseous samples 152. Gaseous samples 152 are channeled to thediffuser region portion of ion trap reactor 108 for expanding gaseoussamples 152 prior to entry into the ionization chamber portion of iontrap reactor 108. ⁶³Ni emits low-energy β-particles into ion trapreactor 108 and the β-particles ionize samples 152 while in the gaseousphase, thereby forming positive ions, negative ions, and free electrons.Ion trap reactor 108 is substantially a field-free region. Therefore,increasing a population density of the ions and electrons within iontrap reactor 108 is facilitated as a function of the flux ofβ-particles. As the ions are being generated in ion trap reactor 108 toincrease the stored ion population 154 therein, retaining grid 110 ismaintained at a slightly greater potential than the potential of iontrap reactor 108 to induce a retention field and reduce the potentialfor ion leakage from ion trap reactor 108. An electric field is theninduced across ion trap reactor 108 and, depending on the polarity ofthe induced electric field, the positive ions or the negative ions arepulsed from ion trap reactor 108, through a high-voltage “kickoutpulse”, and injected into first drift field region 116 through retaininggrid 110. The ions of the opposite polarity are attracted to the wallsof ion trap reactor 108 and are discharged there. The pulses arecontrolled through ITMS control system 144.

First drift field region 116 extends from retaining grid 110 to firstion shutter 128. For those systems that use negative ions, annularelectrodes E1 through E7 are energized to voltages that are sequentiallyless negative between retaining grid 110 to first ion shutter 128,thereby inducing a constant positive field. Motion is induced in thenegative ions from the initial pulse in ion trap reactor 108 and theions are channeled through first drift field region 116 to first ionshutter 128. First ion shutter 128 induces a voltage that is lessnegative than the voltage of electrode E1 and is more negative than thevoltage of electrode E7. ITMS control system 144 regulates thevelocities of the ions injected from ion trap reactor 108 as they driftthrough first drift field region 116 toward first ion shutter 128 suchthat a selected portion 156 of ions injected into region 116 arrive atshutter 128 at a predetermined time, while a substantial amount of anon-selected portion 158 of ions arrive later due to the slowervelocities or faster (not shown) due to the higher velocities. As such,ITMS control system 144 regulates the voltage of first ion shutter 128for a first predetermined temporal period, thereby injecting asubstantial amount 160 of the selected portion 156 of ions from firstdrift field region 116 into fragmentation region 118. A significantamount of the non-selected portion 158 of ions are not permitted totransit through first ion shutter 128 when the voltage is again adjustedby ITMS control system 144 to block such ions and molecules that aresubsequently discarded, thereby reducing injection of the non-selectedportion of ions and into fragmentation region 118.

Also, in operation, ITMS control system 144 regulates electric fieldgeneration device 120 to modify the selected portion of ions, therebygenerating predetermined ion fragments 162 within fragmentation region118 through regulating a voltage and frequency of the controllableelectric field generated between electrodes 124 and 126. The electricfield dissociates a first portion of the selected portion 160 of ionsinjected into fragmentation region 118 into a first portion 164 of thepredetermined ion fragments for further transmission to second fielddrift region 132. Fragmentation of selected ions 162 generates ionfragments 164 that have a different mobility from unmodified ions 166that generate different peaks on the associated output spectrum. Assuch, fragmentation facilitates distinguishing between two different,but intermingled ion populations that would otherwise have similarmobilities, since the modified versions of these fragment ions 164 willhave dissimilar mobilities from those of unmodified ions 166.

Further, in operation, at least some of those ions 168 of thenon-selected portion of ions 158 that made it into fragmentation region118 are also modified to further distinguish the resultant dissociatednon-selected ions 170 from the predetermined ion fragments 162 underconsideration due to the different mobilities. The dissociatednon-selected ions 170 are discarded. In alternative embodiments, none ofthe non-selected ions 158 are dissociated into fragments, but arediscarded regardless.

Moreover, for those embodiments that include optional second ion shutter134, in operation, the selected ion fragments under consideration 164arrive at second ion shutter 134 at different times than most of theother ions, molecules, and fragments due to the different mobilities. Assuch, ITMS control system 144 regulates the voltage of second ionshutter 134 for a second predetermined temporal period, therebyinjecting a substantial amount 172 of the selected portion 164 of thepredetermined fragmented ions from fragmentation region 118 into seconddrift field region 132. A significant amount of the non-selected portionof ions 170 and fragments 166 are not permitted to transit throughsecond ion shutter 134 when the voltage is again adjusted by ITMScontrol system 144 to block such ions 170 and fragments 166 that aresubsequently discarded, thereby reducing injection of the non-selectedportion of ions 158 into second drift field region 132.

Second drift field region 132 extends from a region between thedownstream side of electrodes 124 and 126, or second ion shutter 134 (ifinstalled), to collector region 148 defined by ion collector 136 andcasing 102. Collector electrode 140 is positioned on the opposite sideof drift field region 112 from electrodes 124 and 126, or second ionshutter 134 (if installed), and is held at, or near, a ground potential.For those systems that use negative ions, annular electrodes E8 throughE14 are energized to voltages that are sequentially less negative thanbetween electrodes 124 and 126, or second ion shutter 134 (ifinstalled), to collector electrode 140, thereby inducing a constantpositive field. For those embodiments that include optional ion trap 135rather than optional second ion shutter 134, such ion trap 135positioned between fragmentation region 118 and second drift fieldregion 132 is configured to provide similar operational results assecond ion shutter 134, i.e., release fragmented ions into second drifttube 130 as an alternative to using a shutter grid.

For such embodiments with second ion shutter 134, ITMS control system144 regulates the voltage of second ion shutter 134 for a secondpredetermined temporal period, thereby injecting a substantial amount172 of the selected portion 164 of fragmented ions from fragmentationregion 118 into second drift field region 132. For those embodimentsthat include optional ion trap 135 rather than optional second ionshutter 134, such ion trap 135 positioned between fragmentation region118 and second drift field region 132 is configured to provide similaroperational results as second ion shutter 134, i.e., release fragmentedions into second drift tube 130 as an alternative to using a shuttergrid. Motion is induced in the negative ions through the graduatedpotential along second field drift region 132. As such, ITMS controlsystem 144 regulates the velocities of the selected portion 172 of thepredetermined fragmented ions 164 injected from fragmentation region 118as they drift through second drift field region 132 toward collectorelectrode 140. The selected portion 172 of the predetermined fragmentedions 164 injected into region 132 arrive at collector electrode 140 at apredetermined time, while any remaining non-selected ions 170 and ionfragments 166 are expected to arrive at a different drift time due tothe different velocities. A significant amount of the non-selectedportion of ions 170 and ion fragments 166 are not permitted to transitthrough second ion shutter 134 (or ion trap 135) when the voltage isagain adjusted by ITMS control system 144 to block non-selected ions 170and ion fragments 166 that are subsequently discarded, thereby reducinginjection of the non-selected 170 portion of ions and ion fragments 166into second field drift region 132.

Therefore, in operation, with, or without second ion shutter 134 (and,similarly, with or without ion trap 135), the selected portion 172 ofthe predetermined fragmented ions 164 drift through second field driftregion 132 to collector electrode 140 through aperture grid 138.Aperture grid 138 induces a voltage that is less negative that thevoltage of electrode E8 and is more negative than the voltage ofcollector electrode 140 that is maintained at substantially groundpotential. Signals representative of the ion population at collectorelectrode 140 are generated and transmitted to spectral analysis device142 to determine the constituents in collected gas samples 152, and adetection spectrum representative of the ion or fragment ions detectedat collector electrode 140 through spectral analysis device 142 coupledto collector electrode 140.

The exemplary embodiment as described above is directed to an ITMSdetection system 100 configured to use negative ions. However, in someembodiments, ITMS detection system 100 is configured to use positiveions. In such embodiments, the electric field induced across ion trapreactor 108 has a polarity to “kick out” the positive ions rather thanthe negative ions such that the positive ions are pulsed from ion trapreactor 108 through the high-voltage “kickout pulse”, and injected intofirst drift field region 116 through retaining grid 110. The ions of theopposite polarity are attracted to the walls of ion trap reactor 108 andare discharged there. Motion is induced in the positive ions from theinitial pulse in ion trap reactor 108. Also, in such circumstances,annular electrodes E1 through E7 are energized to voltages that aresequentially less positive between retaining grid 110 to first ionshutter 128 to facilitate inducing motion in the positive ions such thatthe ions are channeled through first drift field region 116 to first ionshutter 128. First ion shutter 128 induces a voltage that is lesspositive than the voltage of electrode E1 and is more positive than thevoltage of electrode E7. The remainder of ITMS detection system 100 isfurther configured for positive ions rather than negative ions andoperation thereof is executed accordingly.

FIG. 2 is a schematic view of an alternative ion trap mobilityspectrometer (ITMS) detection system 200 (not drawn to scale). System200 is similar to system 100 (shown in FIG. 1) with the difference thatsystem 200 includes a dopant injection system 202 coupled in flowcommunication with fragmentation region 118. Some dopants furtherenhance the specificity of identification of substances, for example,and without limitation, some typical dopants used in trace detection ofexplosives are chlorinated compounds, e.g., in a negative ion mode, andwithout limitation, dichloromethane, hexachloroethane, and chloroform,and, in positive ion modes, and without limitation, acetone andammonia-based compounds, e.g., ammonium carbamate, and anhydrousammonia. Therefore, in operation of system 200, a dopant 204 is injectedinto fragmentation region 118 and at least a portion of injected dopant204 is mixed with the selected portion of ions 160 from first driftfield region 116. Operation of system 200 is similar to that of system100 as described above, with the primary difference of the dopantaltering the population of predetermined fragmented ions 164 and 172with constituents including, without limitation, adducts (not shown).

TOF ion mobility spectrometer (IMS) detection systems (not shown) aresimilar to ITMS detection systems 100 and 200 with one difference of theIMS detections systems is that they do not include ion trap featuresthrough a retaining grid that is maintained at a relatively constantvoltage to trap the ions in the ionization chamber. Rather, IMSdetection systems include an ion gate device (sometimes referred to asan ion shutter), e.g., a Bradbury-Nielsen gate. Similar to retaininggrid 110 of systems 100 and 200, as the ions are being generated in theIMS ionization region to increase the ion current therein, the ion gatedevice is maintained at a relative voltage great enough to substantiallyprevent ion current transmitting into the adjacent drift region. Therelative voltage difference between the ion gate device is thentemporarily removed and the stored ions are pulsed from the ionizationregion into the drift region through the ion gate device. The temporalperiod of gate de-energization is predetermined. The voltage applied ofthe ion gate device is then re-established, thereby substantiallyhalting ion entry from the ionization region into the drift region.Therefore, rather than pulsing the ions through a consistently energizedretaining grid as is done for ITMS systems 100 and 200, in the IMSsystems the ion gate is temporarily de-energized.

FIG. 3 is a graphical view, i.e., graph 300 of exemplary spectra thatmay be produced using ITMS detection systems 100 and 200 (shown in FIGS.1 and 2, respectively). Graph 300 includes a y-axis 302 representativeof ion intensity, i.e., detector response in arbitrary units (au). Also,graph 300 includes an x-axis 304 representative of drift time inarbitrary units (au). In the exemplary embodiment, a sample of ethyleneglycol dinitrate (EGDN) [C₂H₄(ONO₂)₂], a common constituent of explosivedevices, is introduced into IMS detection system 200, system 200including tandem reactive drift tube configuration 112 (shown in FIGS. 1and 2).

Graph 300 includes a first trace 306 representing a spectral analysis ofthe EGDN sample with the fragmentation system off, i.e., electric fieldgeneration device 120 in fragmentation region 118 (both shown in FIGS. 1and 2) removed from service. First trace 306 includes a chloride ion(Cl⁻) peak 308 and a M.Cl⁻ adduct peak 310. While peak 308 is a dopantpeak, peak 310 may indicate the presence of EGDN (EGDN*Cl⁻). A peak 312may indicate the presence of trace amounts of NO₃ ⁻.

Graph 300 also includes a second trace 314 representing a spectralanalysis of the EGDN sample with the fragmentation system on, i.e.,electric field generation device 120 in fragmentation region 118 placedin service. Second trace 314 includes a nitrate (NO₃ ⁻) peak 316 as aresult of the decomposition of EGDN, such peak indicative of thepresence of EGDN. Notably, M.Cl⁻ adduct peak 310 is not found withsecond trace 314 since the M.Cl⁻ ions were decomposed using thefragmentation system. The peak just to the left of nitrate peak 316 isat least partially due to some additional Cl⁻ from peak 308. Therefore,use of the fragmentation system during sample analysis in conjunctionwith the remainder of the tandem reactive dual drift tube and dualshutter configuration 112 significantly improves the sample analyses forsubstances of interest, such as EGDN.

FIG. 4 is another graphical view, i.e., graph 400 of exemplary spectrathat may be produced using ITMS detection systems 100 and 200 (shown inFIGS. 1 and 2, respectively). Graph 400 includes a y-axis 402representative of ion intensity, i.e., detector response in arbitraryunits (au). Also, graph 400 includes an x-axis 404 representative ofdrift time in arbitrary units (au). In the exemplary embodiment, asample of ethylene glycol dinitrate (EGDN) [C₂H₄(ONO₂)₂], a commonconstituent of explosive devices, is introduced into IMS detectionsystem 200, system 200 including tandem reactive drift tubeconfiguration 112 (shown in FIGS. 1 and 2). Only the analyte ions ofEGDN (shown as 310 in FIG. 3), however, are transferred through thefirst shutter 128 into the second drift tube 130 defining the seconddrift region 132 whereas all other ions of different mobilities areexcluded from passing the shutter.

Graph 400 includes a first trace 406 representing a spectral analysis ofthe analyte ions of the EGDN sample with the fragmentation system off,i.e., electric field generation device 120 in fragmentation region 118(both shown in FIGS. 1 and 2) removed from service. First trace 406includes an M.Cl⁻ adduct peak 410, peak 410 may indicate the presence ofEGDN (EGDN*Cl⁻). No other peaks such as the dopant peak previously shownas 308 in FIG. 3 are detected in the spectrum 406 displayed in FIG. 4.

Graph 400 also includes a second trace 412 representing a spectralanalysis of the analyte ions (M.Cl)⁻ of the EGDN sample with thefragmentation system on, i.e., electric field generation device 120 infragmentation region 118 placed in service. Second trace 412 includes anitrate (NO₃ ⁻) peak 414 as a result of the decomposition of the analyteions of EGDN, such peak indicative of the presence of EGDN. Notably,this peak was not present when the fragmentation system was off.Moreover, the intensity of a M.Cl⁻ adduct peak 416 is much lower withsecond trace 412 compared to the intensity of 410 since the M.Cl⁻ ionswere decomposed using the fragmentation system. Therefore, use of thefragmentation system during sample analysis in conjunction with theremainder of the tandem reactive dual drift tube and dual shutterconfiguration 112 significantly improves the sample analyses forsubstances of interest, such as EGDN.

ITMS detection systems 100 and 200 (shown in FIGS. 1 and 2,respectively) facilitate ion fragmentation that further facilitatesidentifying chemical families primarily based on the way the analyteions fragment. In general, ions in a gas phase at ambient pressure arenot as robust as molecules in air at ambient pressure, i.e., theelectrostatic charge on the ions increase the vulnerability of the bondsin the ion to weakening. Also, in general, increasing the thermal energyof the ions increases the vibratory motion, thereby further weakeningthe covalent bonds of the ions and, in cooperation with destabilizingeffects of the ionic charge, rendering the bonds unstable until covalentbond cleavage, i.e., ion fragmentation is achieved. One method ofincreasing the temperature of the gaseous ions is through adding thermalenergy to the gas by increasing the gas temperature through a heatingdevice (not shown) to preheat the gas prior to injection into systems100 and 200. Another method includes using the electric fields inducedas described above to rapidly increase the kinetic energy of the ionsthat translates into increasing the thermal energy, and as such, thevibration of the ions. Use of the electric fields already presentfacilitates weakening of the ion bonds at much lower temperatures.Increasing the strength of the electric fields accelerates ionfragmentation. Because substances of a given family have similarmolecular structures and similar bonding and ionic characteristicswithin the core structure of the molecule, such ions therefore tend tobreak into pieces corresponding to the characteristics of suchsubstance(s). As such, further fragmentation of the ions into selectedand known ion fragments further facilitates identifying chemicalfamilies.

The portable, atmospheric pressure, tandem reactive IMS devicesdescribed herein provide cost-effective systems and methods forimproving detection of materials of interest from an object or person.The systems and methods described herein use a detector having twosequentially arranged drift tubes which are separated by shuttersfacilitating ions of a user-selected, i.e., library-defined drift timeto be introduced into the second drift tube whereas other ions of adifferent mobility are discarded as needed. The IMS and ITMS devicesdisclosed herein facilitate multiple opportunities to isolate ions ofinterest including ion separation and selection in the first drift tube,predetermined modification through fragmentation through a controllableelectric field, and selected transmission into the second drift tubeultimately ending with specific identification of the ions. Regulationof the electric field strength and temperature analyte ions from onecompound may dissociate and form dissociation products that can furtherbe characterized, while ions from another compound may dissociate aswell but form different products or may even not dissociate at all. Assuch, this dissociation information is important for providing anotherdimension of characterizing the mobility of ions by their stability andtheir dissociation products which provides additional confidence in thepresence or absence of peaks that facilitates determining if an alarmcould be generated or rejected. The results are more easily interpretedand provide more definitive information that can be used for thecharacterization of ions since only ions of a particular drift time areexposed to the high electric field and the associated fragmentation.Consequently substantially all dissociation products detected in thesecond drift tube originate from the ions selected from the first drifttube and subsequently fragmented. Moreover, the additional optionalintroduction of dopants facilitates further modification of the selectedions through chemical reactions with or without dissociation. As such,the systems described herein facilitate an additional level ofselectivity that dramatically reduces the false alarm rate from thatobserved on traditional IMS and ITMS systems. Therefore, the portablemobility spectrometers described herein facilitate substance analysiswith higher confidence while maintaining atmospheric pressure operation.

A technical effect of the systems and methods described herein includesat least one of: (a) substantially decreasing the frequency of falsealarms in TOF-IMS and -ITMS detection systems; (b) facilitating ions ofa user-selected, i.e., library-defined drift time to be introduced intoa second drift tube where other ions of a different mobility arediscarded as needed; (c) executing predetermined modification ofselected ions through fragmentation with a controllable electric field;(d) regulating the electric field strength and temperature such thatanalyte ions from one compound dissociate and form dissociation productsthat can further be characterized while ions from other compounds eitherdissociate and form different products or not dissociate at all; (e)increasing dissociation information for further characterizing themobility of ions by their stability and their dissociation products; (f)increasing confidence in the presence or absence of peaks thatfacilitates determining if an alarm could be generated or rejected; and(g) weakening ionic bonds through leveraging weakening of such bonds dueto the electrostatic charge of the ion and increased thermal energy ofthe ion until ion fragmentation into the predetermined ion fragments isachieved, thereby further facilitating identifying chemical familiesprimarily based on the way the analyte ions fragment.

Although specific features of various embodiments of the invention maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the invention, any feature ofa drawing may be referenced and/or claimed in combination with anyfeature of any other drawing.

Some embodiments involve the use of one or more electronic or computingdevices. Such devices typically include a processor, processing device,or controller, such as a general purpose central processing unit (CPU),a graphics processing unit (GPU), a microcontroller, a reducedinstruction set computer (RISC) processor, an application specificintegrated circuit (ASIC), a programmable logic circuit (PLC), a fieldprogrammable gate array (FPGA), a digital signal processing (DSP)device, and/or any other circuit or processing device capable ofexecuting the functions described herein. The methods described hereinmay be encoded as executable instructions embodied in a computerreadable medium, including, without limitation, a storage device and/ora memory device. Such instructions, when executed by a processingdevice, cause the processing device to perform at least a portion of themethods described herein. The above examples are exemplary only, andthus are not intended to limit in any way the definition and/or meaningof the term processor and processing device.

This written description uses examples to disclose the embodiments,including the best mode, and also to enable any person skilled in theart to practice the embodiments, including making and using any devicesor systems and performing any incorporated methods. The patentable scopeof the disclosure is defined by the claims, and may include otherexamples that occur to those skilled in the art. Such other examples areintended to be within the scope of the claims if they have structuralelements that do not differ from the literal language of the claims, orif they include equivalent structural elements with insubstantialdifferences from the literal language of the claims.

1. An apparatus for detecting constituents in a sample, said apparatuscomprising: a first drift tube defining a first drift region; a seconddrift tube defining a second drift region; an ion detector positioneddownstream of said second drift region; a controllable electric fielddevice coupled to said first drift tube and said second drift tube, saidcontrollable electric field device at least partially defining afragmentation region; a first ion shutter positioned between said firstdrift region and said fragmentation region; a spectral analysis devicecoupled to said ion detector, said spectral analysis device configuredto generate a detection spectrum representative of ions detected at saidion detector; and a control system coupled to said controllable electricfield device and said first ion shutter, said control system comprisinga processor, said control system configured to facilitate injection of aselected portion of the predetermined fragmented ions into said seconddrift region, said control system further configured to: regulate saidfirst ion shutter a first predetermined temporal period, therebyfacilitating injection of a selected portion of ions from said firstdrift region into said fragmentation region; and regulate saidcontrollable electric field device to modify the selected portion ofions to generate predetermined ion fragments within said fragmentationregion.
 2. (canceled)
 3. An apparatus for detecting constituents in asample, said apparatus comprising: a first drift tube defining a firstdrift region; a second drift tube defining a second drift region; acontrollable electric field device coupled to said first drift tube andsaid second drift tube, said controllable electric field device at leastpartially defining a fragmentation region; a first ion shutterpositioned between said first drift region and said fragmentationregion; a dopant injection conduit coupled in flow communication withsaid fragmentation region; and a control system coupled to saidcontrollable electric field device and said first ion shutter, saidcontrol system comprising a processor, said control system configured tofacilitate injection of a selected portion of the predeterminedfragmented ions into said second drift region, said control systemfurther configured to: regulate said first ion shutter a firstpredetermined temporal period, thereby facilitating injection of aselected portion of ions from said first drift region into saidfragmentation region; and regulate said controllable electric fielddevice to modify the selected portion of ions to generate predeterminedion fragments within said fragmentation region.
 4. The apparatus inaccordance with claim 1, wherein said control system configured toregulate said first ion shutter a first predetermined temporal period isfurther configured to facilitate discarding a non-selected portion ofions to reduce injection of the non-selected portion of ions into saidfragmentation region.
 5. The apparatus in accordance with claim 4,wherein said control system configured to regulate said controllableelectric field device to modify the selected portion of ions to generatepredetermined ion fragments within said fragmentation region is furtherconfigured to regulate said controllable electric field device todissociate a first portion of the selected portion of ions into a firstportion of the predetermined ion fragments for further transmission tosaid second drift region.
 6. The apparatus in accordance with claim 5,wherein said control system configured to regulate said controllableelectric field device to modify the selected portion of ions to generatepredetermined ion fragments within said fragmentation region is furtherconfigured to regulate said controllable electric field device todissociate non-selected ions into fragments for discarding.
 7. Theapparatus in accordance with claim 5, wherein said control systemconfigured to regulate said controllable electric field device to modifythe selected portion of ions to generate predetermined ion fragmentswithin said fragmentation region is further configured to regulate saidcontrollable electric field device to not dissociate non-selected ionsinto fragments.
 8. The apparatus in accordance with claim 5, whereinsaid control system configured to regulate said controllable electricfield device to modify the selected portion of ions to generatepredetermined ion fragments within said fragmentation region is furtherconfigured to regulate said controllable electric field device tofacilitate weakening of ion bonds in cooperation with an electrostaticcharge of each ion of the selected portion of ions until ionfragmentation into the predetermined ion fragments is achieved.
 9. Theapparatus in accordance with claim 1, wherein said apparatus is atime-of-flight (TOF) ion trap mobility spectrometer (ITMS) detectionsystem, said apparatus further comprising: a casing; an ionizationchamber at least partially defined by said casing, said ionizationchamber configured to generate and store ions, said ionization chambercommunicatively coupled to said control system; and a retaining gridcoupled in flow communication with said ionization chamber and saidfirst drift region, said retaining grid at least partially defining anion trap, said control system further configured to regulate iontransmission into said first drift region through said retaining gridand through pulsing said ionization chamber.
 10. The apparatus inaccordance with claim 1, wherein said apparatus is a time-of-flight(TOF) ion mobility spectrometer (IMS) detection system, said apparatusfurther comprising: a casing; an ionization chamber at least partiallydefined by said casing, said ionization chamber configured to generateand store ions, said ionization chamber communicatively coupled to saidcontrol system; and an ion gate device coupled in flow communicationwith said ionization chamber and said first drift region, said ion gatedevice further operably coupled to said control system, said controlsystem further configured to regulate ion transmission into said firstdrift region through pulsing said ionization chamber and de-energizingsaid ion gate device.
 11. (canceled)
 12. The apparatus in accordancewith claim 1 further comprising a second ion shutter positioned betweensaid fragmentation region and said second drift region, wherein saidcontrol system is further coupled to said second ion shutter, saidcontrol system further configured to regulate said second ion shutter asecond predetermined temporal period, thereby further facilitatinginjection of a selected portion of the predetermined fragmented ionsinto said second drift region.
 13. The apparatus in accordance withclaim 1 further comprising an ion trap positioned between saidfragmentation region and said second drift region, wherein said controlsystem is further coupled to said ion trap, said control system furtherconfigured to regulate said ion trap a second predetermined temporalperiod, thereby further facilitating injection of a selected portion ofthe predetermined fragmented ions into said second drift region.
 14. Amethod of detecting constituents in a sample, said method comprising:channeling a sample gas stream to be tested for constituents into anionization region; generating a plurality of ions in the ionizationregion; injecting at least a portion of the ions from the ionizationregion into a first drift region; injecting a selected portion of ionsfrom the first drift region into a fragmentation region comprisingregulating a first ion shutter a first predetermined temporal period,the first ion shutter positioned between the first drift region and thefragmentation region; and modifying the selected portion of ions,thereby generating predetermined ion fragments within the fragmentationregion comprising regulating a controllable electric field devicepositioned within the fragmentation region.
 15. The method in accordancewith claim 14 further comprising injecting a dopant into thefragmentation region and mixing at least a portion of the injecteddopant with the selected portion of ions from the first drift region.16. The method in accordance with claim 14, wherein regulating a firstion shutter a first predetermined temporal period comprises discarding anon-selected portion of ions, thereby reducing injection of thenon-selected portion of ions into the fragmentation region.
 17. Themethod in accordance with claim 16, wherein regulating the controllableelectric field device positioned within the fragmentation regioncomprises regulating the controllable electric field device todissociate a first portion of the selected portion of ions into a firstportion of the predetermined ion fragments for further transmission tothe second drift region.
 18. The method in accordance with claim 17,wherein regulating the controllable electric field device positionedwithin the fragmentation region further comprises dissociatingnon-selected ions into fragments for discarding.
 19. The method inaccordance with claim 17, wherein regulating the controllable electricfield device positioned within the fragmentation region furthercomprises not dissociating non-selected ions into fragments.
 20. Themethod in accordance with claim 17, wherein regulating the controllableelectric field device positioned within the fragmentation region furthercomprises weakening ion bonds in cooperation with an electrostaticcharge of each ion of the selected portion of ions until ionfragmentation into the predetermined ion fragments is achieved.
 21. Themethod in accordance with claim 14, wherein injecting at least a portionof the ions from the ionization region into a first drift regioncomprises: storing the ions in the ionization region; and regulating ioninjection into the first drift region through a retaining gridcomprising pulsing the ionization region.
 22. The method in accordancewith claim 14, wherein injecting at least a portion of the ions from theionization region into a first drift region comprises: storing the ionsin the ionization region; and regulating ion injection into the firstdrift region through pulsing the ionization chamber comprisingde-energizing an ion gate device.
 23. The method in accordance withclaim 14 further comprising transmitting the selected portion of thepredetermined fragmented ions through the second drift region to an iondetector.
 24. The method in accordance with claim 23 further comprisinggenerating a detection spectrum representative of the ions detected atthe ion detector through a spectral analysis device coupled to the iondetector.
 25. The method in accordance with claim 23, whereintransmitting the selected portion of the predetermined fragmented ionsthrough the second drift region comprises regulating a second ionshutter a second predetermined temporal period, the second ion shutterpositioned between the second drift region and the fragmentation region.26. The method in accordance with claim 23, wherein transmitting theselected portion of the predetermined fragmented ions through the seconddrift region comprises regulating an ion trap a second predeterminedtemporal period, the ion trap positioned between the second drift regionand the fragmentation region.